1. Field of the Invention
The present invention relates to systems that store data on optical media such as optical disks. More particularly, the invention concerns a system to monitor the power used while writing data to an optical medium to detect media and lens contamination, and take appropriate remedial action when contamination is found.
2. Description of the Related Art
Modern computers frequently store data on optical media such as optical disks. FIG. 1 illustrates a typical optical disk storage system 100, in which a laser beam 102 writes data to an optical disk 104. A laser device 106 generates the laser beam 102 and directs the beam 102 through an adjustable focusing lens 108. In many cases, the laser device 106 comprises a semiconductor laser. The system 100 also includes various circuitry embodied in a controller 110, which determines the power, frequency, and other operational characteristics of the laser device 106.
To successfully write data to optical media, the laser beam 102 must contain sufficient power to heat the media and thereby effect a "state change." Therefore, in a typical system 100 the controller 110 calibrates the laser device 106 to ensure that the laser beam 102 contains a sufficient level of power to write data to the disk 104. Some systems calibrate the laser device 106 by imparting the laser beam 102 upon a designated area (not shown) of the disk 104 and then measuring the disk's reflectivity. Then, in accordance with the measured reflectivity, the controller 110 performs calculations to determine an appropriate power level at which to operate the laser device 106. The controller 110 stores this value in a memory 112, in the form of a digital electrical signal. Skilled artisans refer to this digital signal as the "write-calibration laser DAC value", or "W/C" value for short. The memory 112, for example, may comprise random access memory ("RAM"). To write data to the disk 104 after the system is calibrated as described above, a laser driver 114 retrieves the digital W/C value from the memory 112, converts it to an analog control signal, and feeds the analog control signal to the laser device 106 to determine its power.
Other calibration systems also exist. For example, some systems perform a series of data writes and data reads to/from the disk 104 while counting the errors that occur. Then, the controller 110 uses the number of counted errors to compute a W/C value. The controller 110 stores the computed W/C value, and uses it to drive the laser device 106 as mentioned above. Engineers have developed various other calibration techniques, in addition to those mentioned above.
In many respects, these systems have satisfied most users' expectations. However, even if these systems perform calibration correctly, contamination of the disk 104 and/or the lens 108 can still cause errors. When the disk 104 and lens 108 are uncontaminated, the laser device 106 can successfully write to the disk 104 using a power level of 5-7 mW (as an example). However, dust and other particles may adhere to the disk 104 and/or lens 108 over time, gradually contaminating them. This contamination reduces the laser beam's effectiveness in writing data to the disk 104. Therefore, with more contamination, the laser device 106 must produce a more powerful laser beam 102.
When contamination reaches a certain level, the required power exceeds the available power, i.e. the maximum power capability of the laser device 106. The maximum available power for some laser devices may be about 12.5 mW, for example. At this point, the laser device 106 cannot produce a laser beam capable of reliably writing to the disk 106. In some cases, failure of the drive to write data can be catastrophic. For example, all files on a disk may be lost if the data to be written involves critical data such as file allocation tables.